A recent report from Oregon State University paints a worrying picture of declining oxygen levels in the waters of the Pacific Northwest over the years. Scientists are sounding the alarm about the disastrous consequences for the region's marine ecosystems and fisheries.
Oxygen levels at their lowest near the seabed
The report finds that waters off Washington, Oregon and northern California reached extremely low levels of dissolved oxygen near the seabed in 2021. These hypoxic areas, where oxygen is running low, represent a direct threat to many marine species that live or feed there.
However, researchers noted significant regional disparities in oxygen levels:
The influence of oceanographic processes on water oxygenation
Professor Jack Barth, an oceanographer at OSU and lead author of the study, explains these regional differences by specific oceanographic processes. On the narrow continental shelf of southern Oregon, deep, oxygen-poor waters are more easily drained and replaced by better-oxygenated waters. Conversely, on the broader continental shelves of central Oregon and Washington, waters stagnate longer, maintaining dangerously low oxygen levels near the seafloor.
The role of climate change in oxygen depletion
If the natural process of upwelling, which brings deep waters rich in nutrients but poor in oxygen towards the coasts, is at the origin of the depletion of oxygen, climate change is now exacerbating this phenomenon. The warming of land relative to the oceans causes stronger and more persistent southerly winds, which keep oxygen-poor waters in place and hinder renewal by better oxygenated waters.
Furthermore, the decomposition of organic matter from phytoplankton, which proliferates thanks to the nutrients provided by upwelling, consumes more oxygen in the bottom waters. A vicious circle sets in, which the natural processes of mixing and circulation of water find it increasingly difficult to counterbalance.
A major challenge for fisheries and marine ecosystems
The consequences of these low oxygen levels on marine fauna are already visible, including dead crabs hauled up in fishing nets in certain areas. But the real impact on fish and other exploited species remains difficult to assess without direct observations by cameras or trawls.
Researchers agree, however, that hypoxia represents a major challenge for the species on which fisheries depend. Studies are underway to better understand and quantify the effects of this phenomenon on ecosystems and fishing activities in the region.
Given the urgency of the situation, it is crucial to deepen our understanding of the complex interactions between climate change, ocean processes and marine life. Only resolute action to limit global warming, combined with adaptive management of fisheries, will preserve the health of the oceans and the precious resources they contain for future generations. Time is running out, and each year that passes without significant progress brings these marine ecosystems one step closer to a potentially catastrophic point of no return.
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